ABSTRACT: Holocene limnologic and climatic change in Québec-Labrador, as inferred from freshwater diatoms and chironomids

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Abstract

The knowledge of Holocene climatic trends in northern Québec and Labrador relies primarily on paleobotanical evidence, and little is known about aquatic ecosystem evolution in this remote northern region. In order to provide more detailed paleoclimatic data and to test hypotheses as formulated by palynological studies, we adopted a multidisciplinary paleolimnological approach that investigates the time-course of changes in freshwater versus terrestrial ecosystems during periods of rapid climate change, including the deglaciation and late Holocene. Our study involves close-interval analyses of fossil diatoms and chironomids on a series of 3 sediment cores, also analysed for pollen and macrofossils, from sites located along a latitudinal and ecoclimatic transect across the Québec-Labrador Peninsula (latitude 51°-58°N). Transfer functions already developed for the study region were used to infer surface water temperature trends from fossil chironomids as well as alkalinity and water colour from fossil diatoms. These quantitative tools are useful to reconstruct past limnologic fluctuations closely associated with climatic changes and vegetational shifts in lake catchments, which help clarify aquatic-terrestrial linkages. A chironomid-based temperature reconstruction for the northernmost of the three study sites (Kangiqsualujjuaq), revealed substantial changes in the water temperature regime in the history of this lake (range of 10° to 18°C). Diatom-based reconstructions of alkalinity and water colour will also be presented. Preliminary results with respect to climate dynamics and aquatic ecosystem response in the region since deglaciation will be discussed.

Bibliography of Canadian Geomorphology